1. Field of the Invention
The present invention relates to a rolling bearing. More particularly the present invention relates to a rolling bearing in which a hard film, having a predetermined structure, which contains diamond-like carbon is formed on a raceway and a sliding contact surface of a cage.
2. Description of Related Art
A hard carbon film is a hard film called diamond-like carbon (hereinafter referred to as DLC. Film/layer containing DLC as its main component is also called DLC film/layer). Various naming is given to the hard carbon. For example, it is called a hard amorphous carbon, amorphous carbon, hard amorphous-type carbon, i-carbon, and diamond-shaped carbon. These terms are not clearly distinguished from one another.
As the essential quality of the DLC, the DLC has a structure in which diamond and graphite are mixed with each other and is thus the structure is intermediate between that of the diamond and that of the graphite. The DLC has a high hardness almost equal to that of the diamond and is excellent in its wear resistance, solid lubricating property, thermal conductivity, chemical stability, and corrosion resistance. Therefore the DLC is utilized as protection films of dies, tools, wear-resistant mechanical parts, abrasive materials, sliding members, magnetic and optical parts. As methods of forming the DLC film, a physical vapor deposition (hereinafter referred to as PVD) method such as a sputtering method and an ion plating method; a chemical vapor deposition (hereinafter referred to as CVD) method; and unbalanced magnetron sputtering (hereinafter referred to as UBMS) method are adopted.
Attempts are made to form the DLC film on the raceway of a bearing ring of a rolling bearing, the rolling contact surface of a rolling element thereof, the sliding contact surface of a cage thereof. The DLC film generates a very large internal stress when the DLC film is formed. Although the DLC film has a high hardness and Young's modulus, it has a very small deformability. Thus the DLC film has disadvantages that it is low in its adhesiveness to a base material and liable to peel therefrom. Therefore in forming the DLC film on the above-described surfaces of the bearing members of the rolling bearing, it is necessary to improve its adhesiveness to the surface of the base material.
To improve the adhesiveness of the DLC film to the base material by forming the intermediate layer, there is proposed the rolling apparatus. The rolling apparatus has the foundation layer, formed on the raceway groove or the rolling contact surface of the rolling element made of an iron and steel material, which contains any one or more elements selected from among chromium (hereinafter referred to as Cr), tungsten (hereinafter referred to as W), titanium (hereinafter referred to as Ti), silicon (hereinafter referred to as Si), nickel, and iron as its composition; the intermediate layer, formed on the foundation layer, which contains the same constituent elements as those of the foundation layer and carbon such that the content rate of the carbon is larger at the side opposite to the foundation layer than at the side of the foundation layer; and the DLC film, formed on the intermediate layer, which consists of argon and carbon such that the content rate of the argon is not less than 0.02 mass % nor more than 5 mass % (see patent document 1). To improve the adhesiveness of the DLC film to the base material by forming the intermediate layer, there is proposed the cage of the rolling bearing on which a plurality of films is formed such that the intermediate layer having the predetermined hardness is interposed between the film of the uppermost layer and the cage (see patent document 2).
To improve the adhesiveness of the DLC film to the base material by an anchoring effect, there is proposed the rolling bearing in which irregularities whose height is 10 to 100 nm and average width is not more than 300 nm are formed on the raceway by means of ion bombardment process and the DLC film is formed on the raceway (see patent document 3).
In addition, there is proposed the cage composed of the hardened layer, subjected to the predetermined treatment, which is formed on the surface of the base material; the hard film, having a higher hardness than the hardened layer and coating the hardened layer therewith, which is formed on the surface of the hardened layer; and the soft film, having a solid lubrication effect and coating the hard film therewith, which is formed on the surface of the hard film. There is also proposed the method of producing this cage.
Because the rolling bearing in which the fluorine grease is packed is excellent in its high-temperature durability, it is used as a bearing for the engine room of a car and as a bearing for the toner-fixing part of a copying machine, a printer, and the like. In addition, because the fluorine grease-packed rolling bearing is excellent in its vapor pressure property, it is frequently used for vacuum equipments. When a large amount of the fluorine grease is present, it displays a favorable lubricating property. But when the supply of the fluorine grease to a rolling contact portion and a sliding portion is short, and thereby boundary lubrication may occur. As a result, a reaction takes place between perfluoropolyether (hereinafter referred to as PFPE) oil which is the base oil fluorine grease and steel (iron) which is a material of the bearing, with the result that the base oil decomposes and the steel wears and the bearing has a short life. Further because this reaction causes the PFPE oil to deteriorate and consumption thereof to be increased, the amount of a utilizable lubricating agent decreases significantly. Consequently these phenomena have a synergistic effect on the bearing, thus causing the bearing to have a short life and a phenomenon such as seizing to occur.
As means for restraining the reaction between the PFPE oil and the steel, there is proposed the fluorine grease contains the organic compound capable of forming a film on the surface of the metal (see patent document 6). It is conceivable that the reaction between the PFPE oil and the steel can be restrained by coating the steel with the hard film such as the above-described DLC film.